Hey Chevy, are you drawing with the same needle as your injecting? If so you should try to swap needles and use a 21g to draw from vial and then 25g to inject, this is what i do and seems to work well. Have to agree on warming the oil up, i put it in a cup of warm water to do it.
Also after you inject leave the pin in there for a few seconds to let the oil disperse, then remove pin half way out and leave for a further few seconds, this will let the oil move around a bit and hurt a lot less afterwards. And don't forget to massage the area for a few minutes to get the oil moving around.
Good luck man, I'm in week 2 of a similar cycle and loving it. As far as an Aromatase inhibitor (AI) goes it depends on you and your body, i run .25 Arimidex EOD but i have a high BF and am taking Proscar for my hair ( which converts to estro ). I believe most people will say not to use it unless needed but others say its ok, lol, personal choice i suppose.